1. Field of the Invention
The present invention generally relates to video signal switching apparatus and, more particularly, is directed to a video signal switching apparatus for use in a switching apparatus which switches monitor or supervisory video cameras.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 62-142489, for example, describes a supervisory apparatus employing a video camera. In this kind of supervisory apparatus, if supervisory video cameras are installed at a plurality of places, then it is proposed that pictures of the supervisory places are monitored by monitor receivers the number of which corresponds to that of the supervisory video cameras. In this case, however, with the increase of the places to be monitored, the number of the video cameras and that of monitor receivers are increased, which as a result makes the supervisory system complicated in arrangement. Further, if a video signal from a supervisory video camera is recorded on a video tape recorder (VTR) instead of the monitor receiver, there is then the disadvantage that the number of VTRs is increased with the increase of the places to be monitored, which also makes the supervisory system complicated in arrangement.
To avoid these disadvantages, a video signal switching apparatus for a supervisory camera is now commercially available on the market, in which video signals supplied from supervisory video cameras installed on a plurality of supervisory places are selectively switched and supplied to a single monitor receiver.
In this video signal switching apparatus for supervisory cameras, video signals from a plurality of supervisory video cameras connected thereto are sequentially switched at a predetermined interval and then fed to the single monitor receiver. If this video signal switching apparatus is utilized, then the user can monitor all places by a supervisory picture displayed on the picture screen of a single monitor receiver, which simplifies the arrangement of the supervisory system and which makes it possible for the user to carry out the monitoring with ease. Further, when the video signals from the supervisory video cameras are recorded on the VTR, these video signals can be efficiently recorded on the single VTR by utilizing this video signal switching apparatus.
Incidentally, if pictures of a plurality of places to be monitored are sequentially displayed by utilizing this video signal switching apparatus, i.e., if pictures of eight supervisory video cameras are repeatedly and sequentially displayed one second each, then it takes eight seconds for the user to monitor pictures of all supervisory cameras. There is then the disadvantage that the respective places are monitored only during one second at every eight seconds. In order to eliminate this disadvantage, the following proposal is made:
Two video signal switching apparatus and two supervisory receivers are respectively prepared, a plurality of supervisory cameras are divided into two systems, the supervisory cameras of one system are connected to one video signal switching apparatus, the supervisory cameras of the other system are connected to the other video signal switching apparatus and separate monitor receivers are connected to respective video signal switching apparatus. With the above-mentioned arrangement, eight supervisory cameras, for example, are divided into two systems at every four supervisory cameras and pictures of the respective supervisory cameras are switched at every second by the respective video signal switching apparatus, whereby pictures of the respective supervisory cameras are displayed during one second each at every four seconds by the two monitor receivers. Accordingly, the places to be monitored can be monitored at the cycle (frequency) of 1/2 as compared with the case such that the single video signal witching apparatus is utilized.
However, if the places are monitored by the two supervisory systems as described above, two video signal switching apparatus are needed, which unavoidably makes the supervisory system complicated in arrangement.
Furthermore, this kind of supervisory camera video signal switching apparatus is frequently utilized at night in an automated fashion. In this case, although it is proposed that pictures switched by the video signal switching apparatus are recorded by the VTR, the user frequently wants to change the places to be monitored depending upon the day of the week and the time. When the place to be monitored is changed, or when the picture switched by the switching apparatus is changed, then the user must operate the switching apparatus so that the setting conditions such as the switching conditions or the like cannot be changed during the supervisory system is operated in an automated fashion.